1. Field of the Invention
The present invention relates to encrypting method and apparatus, decrypting method and apparatus, and a recording medium in which information encrypted by an encrypting method or an encrypting apparatus is recorded, and, for example, encrypting method and apparatus, decrypting method and apparatus, and a recording medium suitable for use in a system in which information such as video signals, audio signals, data signals or the like is encrypted, the encrypted information is recorded on a recording medium, and the encrypted information is decrypted.
2. Description of the Related Art
When information is encrypted and then recorded on a predetermined recording medium, information is encrypted by using a predetermined encryption key and the encrypted information is recorded on the recording medium. The encrypted information is decrypted by using a decryption key for decrypting the encrypted information recorded on the recording medium.
A cryptosystem employing a key (an encryption key) includes two cryptosystems; a common-key cryptographic scheme and a public-key cryptosystem. In the common-key cryptosystem, a key (encryption key) used upon encryption is the same as a key (decryption key) used upon decryption. For example, of the common-key cryptosystems, a data encryption standard (DES) system is frequently employed. On the other hand, in the public-key cryptosystem, an encryption key and a decryption key are different from each other. In this public-key cryptosystem, the encryption key is opened to the public, but the decryption key is kept secret. In general, such encryption method and decryption method are known.
An encryption method is disclosed in Japanese patent publication No. 60007/1990. According to the method, an encryption key is generated based on a data forming a file to be recorded on a recording medium. Information is encrypted by using the encryption key, and the encrypted information is recorded on the recording medium. The file is reproduced from the recording medium, and a decryption key is generated based on data forming the file. Then, the encrypted information is decrypted by using the generated decryption key.
However, when such encryption method and decryption method are employed, the file used for generating the encryption key is recorded on one portion (sequent regions) of the recording medium, which may allow the file to be duplicated with comparative ease.